Occlusion coils are used to occlude a site within a body lumen, such as a blood vessel or Fallopian tube, within the human body. The coil(s) is typically placed at the desired site within the lumen by means of a microcatheter. The coils are normally made of a radio opaque, biocompatible metal such as platinum, gold, or tungsten. In treating brain aneurysms it is common to place a plurality, typically 4 to 12, of coils within the aneurysm. The coils occlude the aneurysm by posing a physical barrier to blood flow and promoting thrombus formation. Ultimately, through healing of the aneurysm sac and re-endothelialization at the neck of the aneurysm a permanent cure of this condition is achieved.
Stents are members, typically tubular shaped, that are placed within body lumens, such as blood vessels, to expand the lumen, provide structural support to the tissue defining the lumen or otherwise repair a segment of the vessel defined by the lumen. Stents may also be placed within vessels by means of microcatheters.
Synthetic polymer or protein coatings have been applied to occlusion coils to enhance their thrombogenicity and wounds healing properties. Ahuja A. A., et al., AJNR Am J. Neuroradiol 14:794-798 (1993) and Dawson, R. C. et al., J. Neurosurgery 36:133 (1995). However, as indicated above, endovascular occlusion techniques generally use small diameter microcatheters to deliver these coils to the occlusion site. Simple polymeric coatings, therefore, result in the problem of increasing the diameter of the coils, which, in turn, may cause them to stick within the microcatheter lumen as they are being delivered. Also, once delivered the coating is subjected to fluid flow within the vessel. If the coating is not solidly fixed to the coil surface it may be dislodged and thus become a potential source of distal thromboemboli.
Ion implantation is a process by which ions are accelerated to a target at energies high enough to bury them below the target's surface. Ion implantation has been applied to the surface of a silicone polymers to alter the thrombogenic properties of the polymer. U.S. Pat. No. 5,152,783. It has also been applied to the surface of polymers such as polystyrene, polyurethane, and extracellular matrix proteins to alter the cellular adhesion properties of the polymer surface. U.S. Pat. No. 5,308,704 and Suzuki, Y. et al., Nucl. Instr. Meth. B. 91:588-592 (1994).